IdentificationThis clam has blue-tinged siphons tipped with orange; often only the siphons will be visible protruding from a rock crevice while the shell remains unseen. The flattened shell valves often appear deformed and are covered in a golden brown to greenish periostracum. The shell can get up to 10 cm long and gapes at the posterior end (click here for information on shell orientation).

Habitat & RangeThe rock endostema is found in holes and crevices in rocks. It often developes within these enclosed areas and so its growth conforms to the shape of the space available. It is also found attached to giant barnacles and kelp holdfasts. It inhabits the low intertidal and subtidal to a depth of 20 m. Its range extends from northern Alaska to northern Mexico.

Similar SpeciesIf only the siphons are visible, with the rest of the shell wedged between rocks, the pair of siphons may be mistaken for a tunicate.